When you represent both sides on a deal the sales volume "doubles". The reason for this is that actually, you have two separate transactions in one: one for the listing side and one for the buying side. This is how the system supposed to operate. If you do not want the sales volume to "double" you can change it. The way to do it is to go to the appropriate transaction under the Commissions tab, select the required side and click the Award allocation button.
Set the filter of sales volume to "entered manually" and adjust it to $ 0.
All commission information will stay the same, the only thing that will change is the sales volume.
Adjustment of sales volume won't reflect on the information shown at the transaction information page. Sales volume will remain "doubled".
But the reports will show updated sales volume.